Structure and stability of solid Xe(H2)n.

Area of Science:

• Materials Science
• High-Pressure Physics
• Solid-State Chemistry

Background:

• Van der Waals compounds offer unique properties.
• Understanding guest-host interactions in clathrates is crucial.
• High-pressure synthesis enables novel material discovery.

Purpose of the Study:

• To investigate the structural behavior of xenon and molecular hydrogen mixtures under high pressure.
• To characterize the formation and stability of novel van der Waals compounds.
• To explore pressure-induced phase transitions and their impact on stoichiometry.

Main Methods:

• Synchrotron X-ray diffraction (single crystal) was employed to determine crystal structures.
• Raman spectroscopy was used to analyze vibrational properties.
• High-pressure synthesis and quenching techniques were utilized.

Main Results:

• A series of hexagonal van der Waals compounds of xenon and molecular hydrogen were formed at 300 K.
• Below 7.5 GPa, Xe(H2)8 crystallizes in a P3̄m1 structure with pressure-dependent xenon atom occupancy.
• A phase transition to an R3 structure occurs with changes in xenon site occupancy, maintaining a fixed 1:8 Xe:H2 stoichiometry.
• The compound can be synthesized at 4.2 GPa, quenched to ambient pressure, and retained up to 90 K.

Conclusions:

• Novel hexagonal van der Waals compounds of Xe and H2 can be synthesized under high pressure.
• Pressure-induced structural changes, including site occupancy variations, are observed.
• These hydrogen-bearing compounds exhibit remarkable stability, allowing retention at ambient pressure after synthesis.